The present invention is generally directed to toner processes, and more specifically, to aggregation and coalescence processes for the preparation of toner resins, especially polyesters, and toner compositions thereof. In embodiments, the present invention is directed to the economical preparation of toners and toner resins without the utilization of the known pulverization and/or classification methods, and wherein in embodiments toner compositions with a volume average diameter of from about 1 to about 25, and preferably from 1 to about 10 microns, and narrow GSD of, for example, from about 1.16 to about 1.26 as measured on the Coulter Counter can be obtained. The resulting toners can be selected for known electrophotographic imaging, printing processes, including color processes, and lithography. More specifically, with the processes of the present invention the use of surfactants is avoided, nonionic surfactant is not needed to disperse the pigment selected, cationic surfactant is not needed to disperse the aggregated particles formed, washing to remove surfactants is eliminated, heating to 20.degree. C. to 40.degree. C. above the resin Tg may be avoided, and the use of additional anionic surfactant may be avoided for stabilization of the aggregated particles formed prior to coalescence. The process of the present invention enables the utilization of polymers obtained by the emulsion free radical polymerization such as polystyrene-(meth)acrylates, poly(meth)-acrylates, and like, and wherein these particles are stabilized by a sodio sulfonated polyester dispersion, such as disclosed in U.S. Pat. No. 5,593,807, the disclosure of which is totally incorporated herein by reference, and wherein the toner particles are then generated by aggregating the aforementioned emulsion and a pigment with an alkali salt, such as magnesium chloride or barium chloride, followed by heating to coalesce the aggregate to toner sized particles ranging, for example, from about 3 to about 9 microns in diameter, and with a geometric distribution of from about 1.12 to about 1.35, and subsequently collecting the toner particles by filtration, optional washing and drying.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, see column 9, lines 50 to 55, wherein a polar monomer, such as acrylic acid, in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. In U.S. Pat. No. 4,983,488, there is disclosed a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component, and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70 are obtained. This process is thus directed to the use of coagulants, such as inorganic magnesium sulfate, which results in the formation of particles with a wide GSD. In U.S. Pat. No. 4,797,339, there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the '127 patent certain polar resins are selected, and wherein flocculation as in the present invention is not believed to be disclosed; and U.S. Pat. No. 4,558,108, discloses a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization. Other prior art that may be of interest includes U.S. Pat. Nos. 3,674,736; 4,137,188 and 5,066,560.
In U.S. Pat. No. 5,290,654, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toners comprised of dispersing a polymer solution comprised of an organic solvent and a polyester, and homogenizing and heating the mixture to remove the solvent and thereby form toner composites. Additionally, there is illustrated in U.S. Pat. No. 5,278,020, the disclosure of which is totally incorporated herein by reference, a process for the preparation of a toner composition comprising the steps of
(i) preparing a latex emulsion by agitating in water a mixture of a nonionic surfactant, an anionic surfactant, a first nonpolar olefinic monomer, a second nonpolar diolefinic monomer, a free radical initiator and a chain transfer agent;
(ii) polymerizing the latex emulsion mixture by heating from ambient temperature to about 80.degree. C. to form nonpolar olefinic emulsion resin particles of volume average diameter of from about 5 nanometers to about 500 nanometers;
(iii) diluting the nonpolar olefinic emulsion resin particle mixture with water;
(iv) adding to the diluted resin particle mixture a colorant or pigment particles, a sodio sulfo polyester resin and optionally dispersing the resulting mixture with a homogenizer;
(v) adding a cationic surfactant to flocculate the colorant or pigment particles to the surface of the emulsion resin particles;
(vi) homogenizing the flocculated mixture at high shear to form statically bound aggregated composite particles with a volume average diameter of less than or equal to about 5 microns;
(vii) heating the statically bound aggregate composite particles to form nonpolar toner sized particles;
(viii) halogenating the nonpolar toner sized particles to form nonpolar toner sized particles having a halopolymer resin outer surface or encapsulating shell; and
(ix) isolating the nonpolar toner sized composite particles.
Furthermore, in U.S. Pat. No. 5,593,807, the disclosure of which is totally incorporated herein by reference, there is illustrated a surfactant free process comprised of forming a latex of a polyester, such as a sodium sulfonated polyester resin in water, mixing the latex with a pigment dispersion containing an alkali halide, such as calcium chloride, to form aggregates, and thereafter heating the formed aggregates to enable the generation of coalesced toner particles which are then filtered off and dried without washing, or with minimal washing. In the present invention, the sodio sulfopolyester resin is primarily utilized as a stabilizer for the generation of an emulsion latex comprised, for example, of a styrene-butadiene-acrylic acid, a styrene-(meth)-acrylate-acrylic acid or an alkyl (meth)-acrylate-acrylic acid, without the use of known nonionic or ionic surfactants, followed by aggregating the emulsion latex with a pigment dispersion and alkali (II) halide, such as magnesium chloride or barium chloride, and followed by heating to afford coalesced toner particles. The advantages associated with the toner process of this invention are, for example, that styrene or acrylate based toner resins are obtained without the use of surfactants, thus minimizing waste and excess washing steps of the toner.
Emulsion/aggregation processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. No. 5,290,654, U.S. Pat. No. 5,278,020, U.S. Pat. No. 5,308,734, U.S. Pat. No. 5,346,797, U.S. Pat. No. 5,370,963, U.S. Pat. No. 5,344,738, U.S. Pat. No. 5,403,693, U.S. Pat. No. 5,418,108, U.S. Pat. No. 5,364,729, and U.S. Pat. No. 5,346,797.
There is a need for an improved emulsion-aggregation-coalescence process for the preparation of toners with small particle size of from about 3 to about 7 microns in diameter and with narrow size particle distribution, such as from about 1.12 to about 1.35, and which process minimizes or avoids waste byproducts or reagents, such as surfactants, and wherein excessive washing is minimized or avoided. Furthermore, there is a need for styrene, (meth)-acrylate based toner resins, or a mixture of styrene or (meth)-acrylate and a polyester in order to obtain toners of low relative humidity, such as from about 1.2 to about 1.5, low fixing temperatures, such as from about 125.degree. C. to about 145.degree. C., excellent blocking characteristics, such as from about 50.degree. C. to about 65.degree. C., and of high gloss properties, especially for pictorial applications, such as from about 40 to about 80 gloss units as measured using the Gardner gloss metering unit.
These and other needs are obtained by the process of the present invention, which process comprises:
(i) preparing a latex emulsion by agitating in water a mixture of a sodio sulfopolyester, a first nonpolar olefinic monomer, a second polar olefinic monomer, a free radical initiator, and a chain transfer agent;
(ii) polymerizing the latex emulsion mixture by heating from ambient temperature to about 80.degree. C. to form nonpolar olefinic emulsion resin particle composite comprised of an olefinic polymer resin and sulfo polyester resin of volume average diameter of from about 5 nanometers to about 500 nanometers;
(iii) diluting the resulting emulsion resin particle composite mixture with water;
(iv) adding to the diluted resin particle mixture a colorant or pigment, a sodio sulfopolyester resin, and optionally dispersing the resulting mixture with a homogenizer;
(v) adding an alkali (II) halide to the resulting mixture thereby forming a flocculation of resin particle composite and pigment;
(vi) homogenizing the resulting flocculated mixture at high shear to form statically bound aggregated composite particles with a volume average diameter of less than or equal to about 5 microns;
(vii) heating the resulting statically bound aggregate composite particles to form nonpolar toner sized particles; and
(viii) isolating the nonpolar toner sized composite particles by filtration and drying.